This research is designed to study the effects of over- and undernutrition on thyroid hormone physiology and to separate those effects which are related to the diet from those which are associated with change in body weight and to identify, where possible, the physiological and biochemical importance of these changes of thyroid metabolism on fuel economy and nutrition. Studies will be performed in normal and obese human volunteers, and in the laboratory rat. Measurements of serum concentrations of total and free thyroid hormones will be correlated with studies of peripheral thyroid metabolism using turnover rate techniques and thermogenesis, using indirect calorimetry, as well as the pituitary response to thyroid releasing hormone. BIBLIOGRAPHIC REFERENCES: Effect of Composition of the Diet on Thyroid Function in the Rat. O. Tulp, E.S. Horton, E. Danforth, Jr., and P.P. Krupp. Clin. Res. 24(5): 640A, 1977. Effect of Excess Carbohydrate (CHO) and Fat Intake on Resting Metabolism. R.L. Burse, R.F. Goldman, E. Danforth, Jr., E.S. Horton, and E.A.H. Sims. Submitted Amer. Physiol. Society. FASEB 1977, In press.